Automatic tension adjuster for fan belt

ABSTRACT

An automatic tension adjuster for a fan belt which automatically adjusts the tension of a fan belt even at the time of sudden decrease in speed of an associated engine so as to prevent slip, so-called &#34;creak&#34; or the like from occurring between the fan belt and a crank pulley. For this purpose, there is provided an adjusting means (30) for automatically adjusting an amount by which a lever (5) swings in a direction opposite to that in which it has pushed a tension pulley (4) against the fan belt (8) when the rotational speed of the crank pulley (1) suddenly lowers. This adjusting means includes the lever (5), a yoke (10), an adjusting bolt (13), a lock nut (14) and a fixing bracket (20).

TECHNICAL FIELD

The present invention relates to an automatic tension adjuster for a fanbelt which adjusts the tension of a fan belt so as to prevent slip,so-called "creak" or the like from occurring between the fan belt and acrank pulley.

BACKGROUND ART

A conventional device for automatically adjusting the tension of a fanbelt (an automatic tensioner) will be described with reference to FIGS.4 and 5. In the drawings, numeral 101 indicates a crank pulley, which isfirmly attached to the tip end of the crankshaft of an engine (notshown). Numeral 102 indicates a fan pulley, which is rotatably attachedto the tip end of an shaft firmly attached to a bracket of an enginefront cover (not shown), and to an end surface of which a fan 103 isattached. Numeral 104 indicates a tension pulley, which is rotatablyattached to the tip end of a lever 105 fitted onto a shaft section 106firmly attached to the bracket of the engine front cover (not shown) andadapted to make a swing motion. Further, a coil spring 107 is woundaround the shaft section 106 of the lever 105, and, by the reactionforce of this coil spring, the tension pulley 104 is pushed against abelt 108, thereby imparting tension to the belt 108.

The operation of this device will now be described. During normaloperation of the engine, the belt 108 is driven by the crank pulley 101,and, due to the resistance of the fan 103, a belt portion 108a receivesa tensile force and tightens, whereas a belt portion 108b slackens.However, the tension pulley 104 moves in the direction of the arrow Fdue to the action of the coil spring 107 attached to the shaft section106, and pushes the belt portion 108b to impart tension thereto, so thatno slackening occurs. If the engine suddenly accelerates, theacceleration time is long, so that the tension pulley 104 follows thebelt portion 108b to impart tension thereto, thus preventing slackening.

At the time of sudden deceleration of the engine, the deceleration timeis short, so that the tension pulley 104 cannot follow the belt portion108b. Further, while the crank pulley 101 on the driving side rapidlydecelerates, the fan pulley 102 on the driven side cannot deceleraterapidly due to the inertia of the fan 103, with the result that the fanpulley 102 is turned to the driving side and the crank pulley 101 to thedriven side. As a result, the belt portion 108a becomes the slack side,and the belt portion 108b the tight side. Due to the tight belt portion108b, the tension pulley 104 moves in the reverse direction R, therebycausing the belt portion 108a to further slacken. As a result, the crankpulley 101 and the belt 108 become liable to slip and cause so-called"creak."

The present invention has been made with a view to solving the aboveproblem. It is accordingly an object of the present invention to providean automatic tension adjuster for a fan belt which adjusts the tensionof a fan belt even at the time of sudden decrease in speed of the engineso as to prevent slip, so-called "creak" or the like from occurringbetween the fan belt and a crank pulley.

DISCLOSURE OF THE INVENTION

In accordance with the present invention, there is provided an adjustingmeans for automatically adjusting an amount by which a swingable leverrotatably supporting a tension pulley at one end and having a coilspring swings in a direction opposite to that in which it pushes thetension pulley against the fan belt when the rotational speed of thecrank pulley suddenly lowers as a result of sudden decrease in speed ofthe engine. This adjusting means comprises a lever having a pin, a yokehaving an elongated hole into which the pin is fitted with some playtherebetween, an adjusting bolt threadedly engaged with the other end ofthis yoke, a lock nut for fastening this bolt onto the yoke, and afixing bracket through which this adjusting bolt passes. Thus, duringnormal operation or at the time of sudden acceleration of the engine,the above-mentioned lever swings in such a manner as to push the tensionpulley against the fan belt to impart tension to the fan belt, so thatno slackening occurs. At the time of sudden deceleration of the engine,on the other hand, the rotational speed of the crank pulley alsodecelerates suddenly, and the abovementioned lever swings in a directionopposite to that in which it pushes the tension pulley. However, sincethe amount of swing motion is adjusted by the above-mentioned adjustingmeans, tension is imparted to the fan belt, so that no slackeningoccurs. Thus, slip, so-called "creak" and the like are prevented fromoccurring between the fan belt and the crank pulley.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a conceptual diagram showing an arrangement of a pulley, belt,yoke, etc. according to the present invention;

FIG. 2 is a partially cutaway view of an automatic tension adjuster fora fan belt according to the present invention in a stopped state or atthe time of sudden deceleration;

FIG. 3 is a partially cutaway view of an automatic tension adjuster fora fan belt according to the present invention during normal operation orat the time of sudden acceleration;

FIG. 4 is a diagram illustrating a pulley, belt, etc. according to aprior-art technique in normal operating condition or at the time ofsudden acceleration; and

FIG. 5 is a diagram illustrating the pulley, belt, etc. according to theprior-art technique at the time of sudden deceleration.

BEST MODE FOR CARRYING OUT THE INVENTION

An embodiment of the present invention will be described in detail withreference to FIGS. 1 to 3.

In FIG. 1, numeral 1 indicates a crank pulley, which is firmly attachedto the tip end of the crankshaft of an engine (not shown) and whichserves as a drive source for transmitting the driving force of theengine to a fan. Numeral 2 indicates a fan pulley, which is rotatablymounted on a shaft firmly attached to a bracket of an engine front cover(not shown), and to an end surface of which a fan 3 is attached. Numeral4 indicates a tension pulley, which is rotatably mounted on the tip endof a lever 5 fitted onto a shaft 6 firmly attached to the engine frontcover bracket (not shown). A pin 9 is firmly attached to the other endof the lever 5. As shown in FIGS. 2 and 3, a torsion coil spring 7 iswound around the shaft 6 of the lever 5. Due to this arrangement, thelever 5 is biased in a clockwise direction, as seen in FIG. 1, so thatthe tension pulley 4 is pushed against the belt 8 to impart tensionthereto. Further, firmly attached to the engine front cover (not shown)is a bracket 20 having a hole through which an adjusting bolt 13 passes.

An adjusting means 30 is attached to the pin 9 of the above-mentionedlever 5. The adjusting means 30 comprises a yoke 10 having at one end anelongated hole 11 adapted to engage with the pin 9 with some playtherebetween and at the other end a threaded section 12, an adjustingbolt 13 threadedly engaged with the threaded section 12 of this yoke, alock nut 14 for fastening the adjusting bolt 13 to the yoke 10, and thebracket 20 through which the adjusting bolt 13 passes. When the engineis in the stopped state, adjustment is performed by using the adjustingbolt 13 threadedly engaged with the threaded section 12 in such a mannerthat the pin 9 of the lever 5 is in contact with the left-hand end ofthe elongated hole 11 of the yoke 10, with the belt 8 properly tightenedby the tension pulley 4. At this time, a head section 15 of theadjusting bolt 13 is in contact with the bracket 20. Subsequently, thelock nut 14 is fastened to integrally connect the yoke 10 and theadjusting bolt 13 (see FIG. 2).

Next, the operation of the present device will be described. In thenormal operating condition of the engine or at the time of suddenacceleration thereof, the belt 8 is driven by the crank pulley 1, and,due to the resistance of the fan 3, a belt portion 8a receives a tensileforce to tighten, whereas a belt portion 8b slackens. However, due tothe action of the coil spring 7 attached to the shaft 6 of the lever 5tending to rotate the lever 5 in the clockwise direction (FIG. 1), thebelt portion 8b is tightened by the tension pulley 4. Further, if, atthe time of sudden acceleration, the belt 8 suddenly expands, the pin 9of the lever 5 moves to the right-hand end of the elongated hole 11 ofthe yoke 10, or further pushes the right-hand end of the elongated hole11 to form a gap 16 between the head section 15 of the adjusting bolt 13and the bracket 20, with the result that lever 5 is allowed to move, andthe action of the tension pulley 4 to tighten the belt 8 is not hinderedby the adjusting means 30 (see FIG. 3).

At the time of sudden decrease in speed of the engine, on the otherhand, the deceleration time is short, and, although the crank pulley 1on the driving side suddenly decelerates, the fan pulley 2 on the drivenside cannot rapidly decelerate due to the inertia of the fan 3. As aresult, the fan pulley 2 is turned to the driving side, and the crankpulley 1 to the driven side, with the belt portion 8a slackening and thebelt portion 8b tightening. The tension pulley 4 is pulled to the sideof the belt portion 8b, and tends to move in a direction to slacken theentire belt 8, i.e., the lever 5 tends to rotate counterclockwise asviewed in FIG. 1 (the direction opposite to that in which it moves atthe time of sudden acceleration). However, since the pin 9 of the lever5 is in contact with the left-hand end of the yoke 10, and the headsection 15 of the adjusting bolt 13 integrally connected to the yoke 10is restricted by the bracket 20, the lever 5 cannot move. Accordingly,the tension pulley 4 continues to tighten the belt 8, and causes noslip. Further, no creak due to slip occurs (see FIG. 2).

As described above, the tension pulley 4 is not restricted in itsmovement during normal operation and at the time of sudden acceleration,and follows the belt 8 to prevent slackening. At the time of suddendeceleration, on the other hand, the movement of the tension pulley 4 isrestricted by the yoke 10 and the adjusting bolt 13, so that the belt 8is prevented from slackening and the generation of slip, so-called"creak" and the like can be prevented.

INDUSTRIAL APPLICABILITY

In accordance with the present invention, there is provided a usefulautomatic tension adjuster for a fan belt which adjusts the tension of afan belt so as to prevent slip, so-called "creak" or the like fromoccurring between the fan belt and a crank pulley.

What is claimed is:
 1. A fan belt apparatus having an automatic tensionadjuster for automatically adjusting the tension of a fan belt duringchanges in the speed of said fan belt; said fan belt apparatus having afan belt stretched between a crank pulley, a fan pulley and a tensionpulley, and a swingable lever which has a coil spring and whichrotatably supports said tension pulley at one end, said coil springbiasing said lever during operation of said fan belt to swing in a firstdirection to push said tension pulley against said fan belt, whereinsaid automatic tension adjuster is equipped with an adjusting meanswhich automatically limits the extent to which said lever is permittedto swing, in the direction opposite to that direction in which saidlever is biased by said coil spring to push said tension pulley, whenthe rotational speed of said crank pulley suddenly lowers.
 2. Anautomatic tension adjuster according to claim 1, wherein said adjustingmeans comprises: said lever having a pin firmly attached to the otherend thereof opposite to said tension pulley; a yoke having an elongatedhole adapter to be engaged with said pin with some play therebetween anda threaded section at the other end portion thereof opposite to saidelongated hole; an adjusting bolt threadedly engaged with the threadedsection of said yoke; a lock nut for fastening said adjusting bolt tosaid yoke; and a fixing bracket through which said adjusting boltpasses.
 3. An automatic tension adjuster for adjusting the tensionduring operation of a belt which passes around a crank pulley, a tensionelement, and a driven pulley; said automatic tension adjustercomprising:a shaft, a lever pivotably mounted on said shaft, said leverhaving a first end portion and a second end portion, said tensionelement being mounted on said first end portion of said lever, a coilspring biasing said lever for rotation in a first direction about saidshaft to push said tension element against said belt to impart tensionto said belt; a bracket; and a mechanical linkage extending between saidbracket and said second end portion of said lever for permitting, duringthe operation of said crank pulley, motion of said second end portion ofsaid lever in said first direction about said shaft, without hinderancefrom the mechanical linkage, to thereby impart tension to said beltduring normal operation of said crank pulley and during suddenacceleration of said crank pulley, said mechanical linkage limiting therotation of said second end portion of said lever about said shaft inthe direction opposite to said first direction at the time of a suddendecrease in speed of said crank pulley, to thereby automatically adjustthe tension of said belt.
 4. An automatic tension adjuster in accordancewith claim 3, wherein said mechanical linkage provides for adjustment ofthe amount by which said lever can rotate about said shaft in adirection opposite to that caused by the bias of said spring.
 5. Anautomatic tension adjuster in accordance with claim 4, wherein thelength of said mechanical linkage is adjustable.
 6. An automatic tensionadjuster in accordance with claim 4, wherein said mechanical linkagecomprises a yoke having a first end portion and second end portion, oneof said first end portion of said yoke and said second end portion ofsaid lever having an elongated hole, the other of said first end portionof said yoke and said second end portion of said lever having a pinmounted thereon and slidably positioned within said elongated hole so asto limit the movement of said lever in a direction opposite to thatcaused by the bias of said spring.
 7. An automatic tension adjuster inaccordance with claim 6, wherein said tension element comprises atension pulley rotatably mounted on said first end portion of saidlever.
 8. An automatic tension adjuster in accordance with claim 7,wherein the length of said mechanical linkage is adjustable.
 9. Anautomatic tension adjuster in accordance with claim 8, wherein saidsecond end portion of said yoke is adjustably mounted to said bracket byan adjusting member which passes freely through an opening in saidbracket, said adjusting member having a first end portion and a secondend portion, said first end portion of said adjusting member beingadjustably secured to said second end portion of said yoke, and a headon said second end portion of said adjusting member positioned on theside of said bracket opposite said first end portion of said adjustingmember to thereby permit limited movement of said adjusting member withrespect to said bracket.
 10. An automatic tension adjuster in accordancewith claim 9, wherein said first end portion of said adjusting member isthreadedly engaged with said second end portion of said yoke.
 11. Anautomatic tension adjuster in accordance with claim 10, wherein saidadjusting member comprises a bolt having a bolt head at one end and athreaded portion at the other end.
 12. An automatic tension adjuster inaccordance with claim 11, wherein said elongated hole is located in saidfirst end portion of said yoke, and said pin is mounted on said secondend portion of said lever.
 13. An automatic tension adjuster inaccordance with claim 12, wherein said lever is mounted on said shaftwith said first end portion of said lever and said second end portion ofsaid lever being on opposite sides of said shaft.
 14. An automatictension adjuster in accordance with claim 13, wherein said spring ismounted about said shaft.
 15. An automatic tension adjuster inaccordance with claim 6, wherein said second end portion of said yoke isadjustably mounted to said bracket by an adjusting member which passesfreely through an opening in said bracket, said adjusting member havinga first end portion and a second end portion, said first end portion ofsaid adjusting member being adjustably secured to said second endportion of said yoke, and a head on said second end portion of saidadjusting member positioned on the side of said bracket opposite saidfirst end portion of said adjusting member to thereby permit limitedmovement of said adjusting member with respect to said bracket.
 16. Anautomatic tension adjuster in accordance with claim 16, wherein saidfirst end portion of said adjusting member is threadedly engaged withsaid second end portion of said yoke.
 17. An automatic tension adjusterin accordance with claim 15, wherein said adjusting member comprises abolt having a bolt head at one end and a threaded portion at the otherend.
 18. An automatic tension adjuster in accordance with claim 6,wherein said elongated hole is located in said first end portion of saidyoke, and said pin is mounted on said second end portion of said lever.19. An automatic tension adjuster in accordance with claim 6, whereinsaid lever is mounted on said shaft with said first end portion of saidlever and said second end portion of said lever being on opposite sidesof said shaft.
 20. An automatic tension adjuster in accordance withclaim 6, wherein said spring is mounted about said shaft.